The present application relates to apparatus and method for withdrawing fluid from a source of fluid such as a pipeline. In preferred arrangements to be described, the apparatus and method is utilised to withdraw oil from an oil pipeline.
The preferred apparatus and method provides means whereby a small quantity of oil may be withdrawn for sampling purposes from an oil pipeline. There have in the past been many problems associated with withdrawal of such small quantities of oil from a pipeline for analysis. For example, it is only necessary to withdraw a few liters in a twenty four hour period from a pipeline which may be passing tens of thousands of tons of oil during that period.
Generally the sampling of the oil is arranged by taking many small grabs of oil over the period of interest and, for example, it has been suggested that one might require ten thousand grabs over a twenty hour period to produce a ten to fifteen liter sample volume so each grab should be 1 to 1.5 cc taken every 7.2 seconds, which might mean that a sample of water was missed.
The mechanical constraints to achieve this reliably and accurately are very considerable. A further difficulty is that it is preferred to withdraw the sample fluid from the pipeline isokinetically, that is, the velocity of the sample passing up the sample pipe should be the same as the velocity of the oil through the pipeline. If a very small quantity of oil is to be taken then this necessitates the use of a very narrow sampling pipe which can clog.